The invention relates to the manufacture of spherical glass objects, in each of which a three-dimensional object is accommodated. A method of this type is known in many embodiments.
It is an object of the invention to design a method such that a very large production speed on industrial scale can be realized wherein the obtained spherical glass articles nevertheless comply with very high technical standards.
It is a further object of the invention to provide a method with which the mass production can take place at very low cost.
The invention generally provides a method of manufacturing successive spherical glass articles, in each of which is accommodated a three-dimensional object or figurine, which method comprises the following steps, to be performed in a suitable sequence, of:
(a) providing a container with a mass of molten glass, which container comprises a discharge opening through which liquid glass can be delivered;
(b) providing thermally resistant figurines;
(c) wholly enclosing successively at least one figurine by molten glass by feeding molten glass thereto from at least two sides; (d) portioning the molten glass before or after step (c) such that molten glass masses are formed, in each of which a figurine is embedded; and
(e) modelling these masses to a spherical form by substantially omnidirectional rolling for a time with simultaneous cooling so that the glass solidifies.
In such a method the problem may occur that air is enclosed in the zone in which the glass masses fed from at least two sides make mutually contact. As a result of the great viscosity of the glass, air or other gas inclusion is no longer able to escape. Air bubbles or other gas inclusions affect to a considerable degree the aesthetic quality of the product for manufacture. It is therefore desirable to perform the method according to the invention such that there is no or only negligible danger of air inclusions. In this respect the method according to the invention can preferably comprise step
(f) performing step (c) substantially in the absence of a gas which cannot dissolve in molten glass, such that gas inclusions, for instance air bubbles, are prevented.
A specific embodiment comprises step
(g) performing step (f) in a gaseous environment under substantial underpressure.
An alternative embodiment of the method comprises step
(h) performing step (f) in the presence of a gas which can dissolve in molten glass, for instance hydrogen, helium, neon, argon.
In order to prevent thermal stresses, the embodiment of the method is recommended which comprises step
(i) performing step (c) after pre-heating the successive figurines, for instance to a temperature in the order of 850xc2x0 C.
A specific embodiment has the special feature that step (e) is performed by means of a first roller in which is recessed a helical groove with a smooth round form, which roller is driven rotatably at a first peripheral speed and co-acts with a second roller driven at a second peripheral speed differing from the first peripheral speed, which second roller is smooth or likewise provided with a helical groove.
A specific embodiment has the special feature that the glass substantially consists of the following constituents:
c. 76% SiO2 
c. 16% Na2O
c. 6% CaO
c. 2% K2O.
A preferred embodiment has the special feature that each figurine is provided beforehand with a glaze coating comprising at least one oxide from the group of which Si, Al, Na, Mg, Zr form part, with colouring pigments on the basis of elements from the group of which Fe, Pb, Cr form part.
A specific embodiment has the special feature that the glazing of the figurines consists substantially of the following constituents:
61.5% SiO2 
14.7% AL2O3 
4.7% Na2O
6.6% K2O
11.2% CaO
1.3% rest
A specific embodiment of the method according to the invention is herein characterized in that the material of the figurines contains the following constituents:
c. 65% SiO2 
c. 19% AL2O3 
c. 1.9% Na2O
c. 4.2% MgO
c. 6.4% CaO
A specific embodiment has the special feature that the material of the figurines consists substantially of a ceramic mass, for instance kaolin (china clay), pipe clay or the like.
It should be understood that the material must be modelled beforehand until it has obtained the desired three-dimensional form. The material can for instance be wetted in powder form, thus resulting in a certain cohesion. A first cohesion is then obtained by a pre-heating, which can take place in a manner to be described below. Only after embedding in the still red-hot plastic glass mass does a definitive hardening of the figurines takes place.
A specific embodiment has the special feature that the material of the figurines contains at least approximately the following constituents:
61.0% SiO2 
21.0% AL2O3 
1.0% FE2O3 
1.2% CaO
0.5% MgO
0.2% Na2O
2.0% K2O
A variant has the special feature that the material of the figurines contains at least approximately the following constituents:
62.0% SiO2 
2.0% AL2O3 
1.1% FE2O3 
0.5% CaO
32.0% MgO
0.7% Na2O
1.0% K2O
In order to avoid thermal stresses, the method according to the invention is preferably performed such that cooling of the spherical articles takes place by progressing through the temperature path from the annealing temperature to the strain temperature at a chosen speed such that cooling takes place in substantially stress-free manner.
The invention further relates to a method which comprises step
(j) annealing after step (e) by again fully heating the spherical glass articles to remove internal stresses and subsequently cooling slowly to for instance about 50xc2x0 C.
A further variant of the method according to the invention comprises the following steps or:
(k) dividing the molten glass delivered via the discharge opening into successive portions;
(l) providing a mould with at least roughly hemispherical bottom and an at least roughly hemispherical cover for placing thereon and removing therefrom;
(m) pouring a first portion of glass onto the bottom;
(n) placing at least one figurine on and optionally partially in this first portion of glass;
(o) pouring a second portion of glass onto the first portion of glass and the figurine;
(p) placing the cover while pressing the thus enclosed mass;
(q) removing the cover;
(r) removing the formed, at least more or less spherical glass mass with figurine enclosed therein; and
(s) performing step (e).
In yet another embodiment the invention provides a method of manufacturing successive spherical glass articles, in each of which is accommodated a figurine, which method comprises the following steps of:
(t) providing a container with a mass of molten glass, which container comprises a discharge opening which can be closed by a valve and into which a vertical tubular central mandrel extends such that a tubular flow of liquid glass can be delivered via the discharge opening;
(u) opening the valve for delivering said flow of liquid glass while simultaneously supplying successive figurines intermittently via the mandrel such that these objects are received in the hollow space of the glass flow;
(v) causing the glass flow to contract and thus embedding the successive objects in the glass mass;
(w) successively separating the lower part of the glass flow in which a figurine is situated such that still molten glass masses are formed, in each of which a figurine is embedded; and
(e) modelling these masses to a spherical form by substantially omnidirectional rolling with simultaneous cooling so that the glass solidifies.
A preferred embodiment has the special feature that the mandrel has a widened lower part which can co-act as valve body with the mouth edge of the discharge opening serving as valve seat.
Yet another embodiment is characterized in that step (c) takes place using a number of concave rollers together bounding a round passage opening.
In some conditions this latter embodiment can advantageously have the special feature that the rollers are driven at an increased peripheral speed reinforcing the contraction of the glass flow. It is noted herein that the rollers in this case have a xe2x80x9cpullingxe2x80x9d function. An effective stretching of the glass flow hereby occurs. In the case where the rollers are driven at a relatively low speed or are slowed down relative to the driving glass flow, a certain expansion occurs upstream relative to the rollers, followed by a contraction as a result of the relatively narrow passage opening defined by the co-acting rollers.
A specific embodiment has the special feature that the rollers have partly spherical cavities co-acting in register positions during rotation.
A practical embodiment has the special feature that step (v) is performed by cutting through the glass flow between the figurines.
This latter embodiment can advantageously be performed such that use is made of two plates with co-acting, generally concave, substantially V-shaped cutting edges.
As already described above, the figurines are preferably pre-heated prior to embedding. The possibility is also described of making use of a mandrel extending through the discharge opening of the glass container. In this embodiment the figurines can be pre-heated simply by making use of a chosen residence time of each figurine in the tubular cavity defined by the mandrel.
Said compositions of glass, figurines and glazing have a number of advantages, particularly in combination with each other. It may for instance be important for the figurines and the glass to have substantially the same thermal coefficient of expansion. This is realized with sufficient precision with the described compositions so that thermal stresses are prevented. The colour-fastness of the glazing must further comply with high standards. These are also fulfilled with the described composition of the glazing.
Finally, the invention relates to a spherical glass article in which a three-dimensional object is embedded, which spherical article with the three-dimensional object embedded therein is manufactured by applying one of the above described methods.
It should be understood that more than one figurine can be embedded in a glass mass. The figurine can be thermally resistant in a manner such that form and colour are wholly retained despite the very high temperature of the glass. Ceramic materials for instance are very suitable in this respect. A glass figurine or a combination of a number of glass figurines can also be envisaged which fuse together to a greater or lesser degree with the encapsulating glass during embedding In this embodiment the contours of the figurine(s) in the finished product are less sharp than in the first described embodiment with for instance a ceramic figurine.